Commercial aircraft are required to provide historical recording of certain flight parameters to enable post accident investigations. These parameters are typically recorded in a flight data recorder system on all commercial aircraft. The recorded parameters are derived from continuous measurements of certain flight inputs during the operational flight of an aircraft. These parameters include functional inputs that are necessary for aircraft accident investigations and accident reconstruction. In the United States, the Federal Aviation Administration issues rules designating the required recording parameters.
In the future, it is expected that additional rules will be promulgated requiring commercial aircraft to include parameters related to the flight control forces. One of these forces includes the forces provided to the aircraft control surface controller interfaces. As used herein, the term “control surfaces” refers to movable aerodynamic surfaces which are operable for maneuvering the aircraft, such as ailerons, rudders, and elevators. Control surface interfaces are the flight deck controls, such as control wheels, rudder pedals, and control columns and their associated electrical and mechanical interfaces.
One force measurement device is described in U.S. Pat. No. 5,195,381 to Keibler. The Keibler device is a force gauge lever that is removably attached to a landing gear control lever for measuring the force applied to the lever. The Keibler device uses a load cell that is directly pushed by the operator of the landing gear. That is to say that the operator pushes the force gauge to transfer the force to the actual landing gear control lever. The Keibler device is not a permanent part of any aircraft systems, but a stand alone device for performing landing gear system maintenance tasks. Also, modern aircraft control surfaces are controlled either by the pilot or the autopilot system. The landing gear lever, in the Keibler device, is controlled by the pilot only. Thus, this device is not adaptable to being integrated into aircraft flight control systems.
Many contemporary commercial transport planes use electrically signaled primary flight control systems, commonly referred to as “fly-by-wire” flight controls. Such fly-by-wire systems have a primary flight control system that receives inputs from the pilot or auto-pilot system. A fly-by-wire flight control system does not include direct mechanical linkages or control cables between the pilot's controls and the aircraft control surfaces, rather the flight deck controller position transducers change the pilot's manual commands of the control wheel, control columns, and rudder pedals to analog electrical signals. These signals are provided to Actuator Control Electronics (ACE), which convert the commands into a digital signal format, and then provided to the Primary Flight Computer (PFC). The PFCs interface with the airplane systems through flight control ARINC 629 buses. The PFCs calculate flight control commands based on flight control laws from the received aircraft systems data. The digital command signals are then provided to ACEs and converted to an analog control signal, which is provided to direct the electro-hydraulic servo actuators that move the control surfaces. The ACEs and electro-hydraulic servo actuators therefore are a control loop that position the control surfaces based on the PFC commands.
Modern flight control systems also include autopilot operations. In autopilot systems, the PFCs receive autopilot commands from the Autopilot Flight Director Computer (AFDC) and process the autopilot commands in the same manner as the manual pilot commands. The autopilot commands are provided to the PFCs via the ARINC 629 bus. The PFCs process and change the autopilot commands to control surface commands and backdrive commands. The control surface commands from the PFCs go to the ACEs to move the flight control surfaces, while the PFCs send backdrive commands to the AFDCs to operate the backdrive actuators. The backdrive actuators move the flight deck controllers (the control wheels, control columns, and rudder pedals) coincident to the control surface movement. In autopilot, therefore, the position transducers of the flight deck control can supply position feedback.
Typical fly-by-wire PFCs utilize airplane systems data such as Air Data Inertial Reference Units (ADIRU), Secondary Attitude Air Data Reference Units (SAARU), and Airplane Information Management Systems (AIMS) to provide stability augmentation, avoid the critical structural modes, increase passenger comfort, and improve the control and handling characteristics of an aircraft. These result in significant benefit in fuel-efficiency, weight-savings, and drag-reduction.
Flight data recorders record these parameters to assist in accident investigation. In a typical aircraft accident investigation, the investigators attempt to determine whether the suspected position of a control surface was commanded by the pilot or by the autopilot system or by other airplane systems. Thus, the force input recording data would allow identification of critical control surface movements and the source of the loss of airplane control. For example, the recorded force data at a recorded time and its corresponding surface position will determine whether the pilot commanded the surface to that position or the surface was commanded by the autopilot system or another airplane system. Thus, investigators would be able to rule out certain factors and focus on other areas.
In order to know if the accident is a training issue or a system issue, the recorder for a control surface controller that integrates a force measurement system should be able to distinguish between systems inputs and pilot or pilots input to the system. It would also be advantageous for a system to permit determining whether the control system jammed. Additionally, it may be desirable to determine if there is a force fight between the pilots.
Accordingly, there is a need in the art for a force measurement system for measuring the pilot control surface interface force input, such as the airplane pitch (control column), roll (control wheel) and yaw (rudder pedals) attitudes. It would also be desirable to avoid major airframe structural changes in existing aircraft when implementing such a system. A force recording system also should be physically adaptable to many airplane models. Finally, it is desirable to employ components that are compatible to existing aircraft systems.